Methods of inhibiting fouling in liquid systems

ABSTRACT

Provided are methods of inhibiting microbial fouling and improving efficiency in biocide dosing in an industrial process containing an aqueous liquid having a biocide demand. In exemplary embodiments, the methods comprise treating an aqueous liquid having a biocide demand with a biocide, monitoring the biocide demand of the aqueous liquid, and filtering a stream of the aqueous liquid. The filtering may be performed in a full-flow or side stream manner.

FIELD

The disclosure is directed to methods of inhibiting fouling in liquidsystems by using biocides and filtration techniques.

BACKGROUND

Throughout the world, there are many different types of industrial watersystems. Industrial water systems exist at least in part so thatnecessary chemical, mechanical, and biological processes can beconducted to reach their desired outcomes. Even the best water treatmentprograms currently available cannot always prevent fouling in industrialwater systems. If an industrial water system is not periodically cleanedto remove contaminants, the industrial water system will almostcertainly become heavily fouled.

Fouling has a negative impact on the industrial water system. Forexample, severe mineral scale (i.e., inorganic material) can build onthe water contact surfaces. Scale on an industrial water system surfacepresents an ideal environment for the growth of microorganisms. Thepresence of microorganisms poses an additional challenge to watertreatment of the industrial water system, as biocides, scale inhibitors,and/or corrosion inhibitors may be necessary to maintain efficientoperation of the industrial water system.

Evaporative cooling water systems are particularly prone to fouling,which can occur via a variety of mechanisms. Non-limiting examples offouling mechanisms include deposition of airborne, water-borne,water-formed, and/or microbiological contaminants; water stagnation;process leaks; and other factors. If fouling is allowed to progress, theindustrial water system can suffer from decreased operationalefficiency, equipment failure, lack of water quality control, andincreased health-related risks associated with microbial fouling.

As previously mentioned, microbiological contaminants may cause fouling.Non-limiting sources of microbiological (i.e., microbial) contaminationare airborne contamination, makeup water, process leaks, and improperlycleaned process equipment. These microbials can establish colonies onany wettable or even semi-wettable surface of the industrial watersystem. Once microbial counts are present in the bulk water, within ashort period of time, more than 99% of the microbes present in the waterwill be present on all surfaces within biofilms.

By design, cooling towers are excellent air scrubbers. As a consequenceof the cooling process, a cooling tower typically flushes airbornecontaminants into the water phase. These contaminants can ultimatelyfind their way to the heat exchanger surfaces, where they becomedeposited, thereby reducing heat transfer. Non-limiting examples of suchcontaminants include particulate matter, organic and inorganiccontaminants, oils, process contaminants, microorganisms, and so forth.Suspended matter in the cooling water provides the microorganisms withreadily available nourishment for sustaining life and reproduction. Itis well established that the presence of inorganic, organic, andmicrobiological deposits have a detrimental impact on the operationalparameters of an industrial cooling system, resulting in reducedefficiency and increased operating cost.

A filtration system can be used to at least partially remove particulatecontaminants and prevent them from reaching concentrations that canadversely impact efficient cooling system operation. The filtrationsystem may be a full-flow in line system or a partial flow side streamsystem. The side stream configuration provides particular advantages tothe full flow system, such as allowing for a smaller filtration unit andthe ability to service off-line while not affecting the cooling process.Generally, the side stream configuration only draws between 2 and 10percent of the flow as compared to the overall circulation of thecooling system.

Any or a combination of several different types of filters may beutilized for the purpose of filtration, and their use depends on thenature of the water and the level of purification wishing to beattained. Non-limiting examples include sand filters, cartridge filters,screen filters, and membrane filters, which may employ ultrafiltration,microfiltration, reverse osmosis, and forward osmosis. Typically in afiltration system, the water to be cleaned wets and passes through theentire filtration surface, with cleaner water leaving the filtrationsystem as filtrate. When sufficient dirt has collected on the filtrationsurface, the filtration surface should be cleaned, thereby restoringperformance. Methods of cleaning the filtration surface depend on thedesign of the filtration device. For example, a cartridge filter is nottypically cleaned but instead replaced. However, a sand or screen filterwill typically undergo a manual or automated backwash cycle to removethe collected contaminants. For membrane filters, there may be similarchemical or non-chemical based cleaning processes, depending on theirdesign.

SUMMARY

In a first exemplary embodiment, the disclosure is directed to a methodof inhibiting microbial fouling. The method comprises providing anindustrial process that contains an aqueous liquid having a biocidedemand and a first filtration surface having a given porosity andoperating variables selected from the group consisting of backwashcount, vacuum count, pressure drop across the first filtration surface,oxidation-reduction potential, and combinations thereof. The aqueousliquid is treated with a biocide. The biocide demand of thebiocide-treated aqueous liquid is determined by monitoring at least oneof the operating variables of the first filtration surface. A stream ofthe biocide-treated aqueous liquid is provided and filtered with thefirst filtration surface to produce a second stream that is initiallyreturned to the industrial process. The filtering and returning arecontinued until a steady state with respect to the first filtrationsurface is reached. Reaching steady state with respect to the firstfiltration surface is then identified, whereupon the stream of thebiocide-treated aqueous liquid is diverted away from the firstfiltration surface to a second filtration surface having a lowerporosity than the first filtration surface. The diverted stream is thenfiltered with the second filtration surface to produce a third stream,and at least a portion of the third stream is returned to the industrialprocess.

In a second exemplary embodiment, the disclosure is directed to a methodof inhibiting microbial fouling. The method comprises providing anaqueous cooling system that contains an aqueous liquid having a biocidedemand. The aqueous liquid is treated with a biocide. At least a portionof the biocide-treated aqueous liquid is diverted to a first filtrationsurface having a given porosity, thereby producing a first stream. Thefirst stream is filtered with the first filtration surface, therebyproducing a second stream. At least a portion of the second stream isfiltered with a second filtration surface that is less porous than thefirst filtration surface, thereby producing a third stream. The biocidedemand of the biocide-treated aqueous liquid is determined by monitoringat least one operating variable for the second filtration surface, theat least one operating variable selected from the group consisting ofbackwash count, vacuum count, pressure drop across the second filtrationsurface, oxidation-reduction potential, and combinations thereof. Atleast a portion of the streams is returned to the aqueous coolingsystem.

In a third exemplary embodiment, the disclosure is directed to anautomated method of improving efficiency in biocide dosing into arecirculation-type aqueous cooling system. The method comprisesproviding a recirculation-type aqueous cooling system that contains anaqueous liquid having a biocide demand. A biocide is dosed into theaqueous liquid at a dosage rate. At least a portion of the biocide-dosedaqueous liquid is diverted into a filtration loop thereby creating afiltration loop stream having a filtration loop flow rate within theaqueous cooling system. The filtration loop stream is sequentiallyfiltered with at least one set of at least two filtration surfacesthereby creating a filtrate. The at least two filtration surfaces areprogressively less porous in a downstream direction. Each of the atleast one set of at least two filtration surfaces has operatingvariables selected from the group consisting of backwash count, vacuumcount, pressure drop across each set of at least two filtrationsurfaces, oxidation-reduction potential, and combinations thereof. Thebiocide demand of the biocide-treated aqueous liquid is determinedeither intermittently or continuously by monitoring at least one of theoperating variables of the at least one set of at least two filtrationsurfaces. A process parameter based on the determined biocide demand isadjusted. The process parameter is selected from the group consisting ofthe dosage rate of the biocide, the filtration loop flow rate, aquantity of the at least one set of at least two filtration surfaces,and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the present disclosure will become more readilyapparent to those of ordinary skill in the relevant art after reviewingthe following detailed description and accompanying drawings, wherein:

FIG. 1 illustrates an exemplary embodiment of a filtration scheme of thedisclosed methods;

FIG. 2 illustrates an exemplary embodiment of a filtration scheme of thedisclosed methods;

FIG. 3 illustrates an exemplary embodiment of a filtration scheme and aset of filtration surfaces within a filter element of the disclosedmethods;

FIG. 4 illustrates an exemplary embodiment of a filtration scheme and aset of filtration surfaces within a filter element of the disclosedmethods;

FIG. 5 graphically illustrates data achieved when practicing anembodiment of a disclosed method;

FIG. 6 graphically illustrates data achieved when practicing anembodiment of a disclosed method.

DETAILED DESCRIPTION

While embodiments encompassing the general inventive concepts may takevarious forms, there is shown in the drawings and will hereinafter bedescribed various embodiments with the understanding that the presentdisclosure is to be considered merely an exemplification and is notintended to be limited to the specific embodiments.

The disclosure is generally directed to filtration techniques useful forreducing or eliminating microbial fouling and/or improving efficiency ofbiocide dosing into aqueous industrial liquids. Application of one ormore of the disclosed filtration techniques may be particularly usefulfor aqueous cooling systems.

As it pertains to this disclosure, “fouling” and “contamination” referto the presence or the deposition of any extraneous or undesirableorganic or inorganic material in a water-containing industrial processor onto one or more surfaces within the water-containing industrialprocess. “Microbial fouling” refers to the presence or deposition of anyextraneous or undesirable microbiological organism in a water-containingindustrial process.

As it pertains to this disclosure, “aqueous cooling system” refers to asystem that uses a water-containing liquid (i.e., aqueous liquid) tocool at least a portion of an industrial process or an enclosed space. Atypical aqueous cooling system may utilize any one or combination of achiller, a cooling tower, and an air washer, to transfer heat energyfrom the water to another substance.

As it pertains to this disclosure, “stream” refers to a flowing liquid.A non-limiting example of a stream is an aqueous liquid flowing througha pipe.

As it pertains to this disclosure, “steady state” generally refers to asituation in which all state variables are statistically constant (e.g.,within a 90% confidence interval of a setpoint or desired value) inspite of ongoing factors that strive to change the variables. For thepresent disclosure, state variables are generally related to filtration(e.g., number of filtration surfaces, pressure drop across at least onefiltration surface, flow rate/flux across at least one filtrationsurface, number of backwash or vacuum cycles per a period of time,etc.), oxidation-reduction potential, and biocide dosage. For example, aparticular filtration reaches steady state when a stream having areasonably constant flow rate reaches a reasonably constant pressuredrop across the filtration surface(s). In certain embodiments, steadystate can be determined when a process has reached statistical processcontrol around one or more setpoints or one or more target values for acertain period of time.

As it pertains to this disclosure, “filtration surface” refers to asection of filtration material where filtration takes place. Afiltration surface may or may not be housed in a filter element. Afilter element (see below) may have one or more filtration surfaceswithin each element. A filtration surface need not be flat.

As it pertains to this disclosure, “filter element” refers to aninterchangeable unit that comprises at least one filtration surface. Incertain embodiments of the methods of the present disclosure, eachfilter element comprises a set of at least two filtration surfaces,wherein the at least two filtration surfaces are progressively lessporous in a downstream direction. For purposes of this disclosure,“cartridge” is a species of the generic “element.”

As it pertains to this disclosure, “biocide” refers to a substance thatis used to kill microbiological organisms or at least inhibitmicrobiological function (e.g., growth and/or reproduction) that may bepresent in a second substance.

As it pertains to this disclosure, “biocide demand” refers to the amountof biocide needed to inhibit microbial fouling, which can be monitoredbased on one or more of several variables described herein.

As it pertains to this disclosure, “automatic,” “automatically,”“automated,” and other similar terms refer to a method or portionthereof that is performed without human intervention or substantiallywithout human intervention. For example, a process carried outautomatically (i.e., an “automated process”) would measure a variableand take action (e.g., change a pump speed, open or close a valve,increase heating or cooling, etc.) based on a comparison of the measuredvariable to a standard value (i.e., a setpoint or a steady statecalculation) without a person having to do anything to make the actiontake place, outside of initially providing all necessary equipment,plumbing, wiring, power, programming, ingredients, and so forth.

In a first exemplary embodiment, the disclosure is directed to a methodof inhibiting microbial fouling. The method comprises providing anindustrial process that contains an aqueous liquid having a biocidedemand and a first filtration surface having a given porosity andoperating variables selected from the group consisting of backwashcount, vacuum count, pressure drop across the first filtration surface,oxidation-reduction potential, and combinations thereof. The aqueousliquid is treated with a biocide. The biocide demand of thebiocide-treated aqueous liquid is determined by monitoring at least oneof the operating variables of the first filtration surface. A stream ofthe biocide-treated aqueous liquid is provided and filtered with thefirst filtration surface to produce a second stream that is initiallyreturned to the industrial process. The filtering and returning arecontinued until a steady state with respect to the first filtrationsurface is reached. Reaching steady state with respect to the firstfiltration surface is then identified, whereupon the stream of thebiocide-treated aqueous liquid is diverted away from the firstfiltration surface to a second filtration surface having a lowerporosity than the first filtration surface. The diverted stream is thenfiltered with the second filtration surface to produce a third stream,and at least a portion of the third stream is returned to the industrialprocess.

In a second exemplary embodiment, the disclosure is directed to a methodof inhibiting microbial fouling. The method comprises providing anaqueous cooling system that contains an aqueous liquid having a biocidedemand. The aqueous liquid is treated with a biocide. At least a portionof the biocide-treated aqueous liquid is diverted to a first filtrationsurface having a given porosity, thereby producing a first stream. Thefirst stream is filtered with the first filtration surface, therebyproducing a second stream. At least a portion of the second stream isfiltered with a second filtration surface that is less porous than thefirst filtration surface, thereby producing a third stream. The biocidedemand of the biocide-treated aqueous liquid is determined by monitoringat least one operating variable for the second filtration surface, theat least one operating variable selected from the group consisting ofbackwash count, vacuum count, pressure drop across the second filtrationsurface, oxidation-reduction potential, and combinations thereof. Atleast a portion of the streams is returned to the aqueous coolingsystem.

In a third exemplary embodiment, the disclosure is directed to anautomated method of improving efficiency in biocide dosing into arecirculation-type aqueous cooling system. The method comprisesproviding a recirculation-type aqueous cooling system that contains anaqueous liquid having a biocide demand. A biocide is dosed into theaqueous liquid at a dosage rate. At least a portion of the biocide-dosedaqueous liquid is diverted into a filtration loop thereby creating afiltration loop stream having a filtration loop flow rate within theaqueous cooling system. The filtration loop stream is sequentiallyfiltered with at least one set of at least two filtration surfacesthereby creating a filtrate. The at least two filtration surfaces areprogressively less porous in a downstream direction. Each of the atleast one set of at least two filtration surfaces has operatingvariables selected from the group consisting of backwash count, vacuumcount, pressure drop across each set of at least two filtrationsurfaces, oxidation-reduction potential, and combinations thereof. Thebiocide demand of the biocide-treated aqueous liquid is determinedeither intermittently or continuously by monitoring at least one of theoperating variables of the at least one set of at least two filtrationsurfaces. A process parameter based on the determined biocide demand isadjusted. The process parameter is selected from the group consisting ofthe dosage rate of the biocide, the filtration loop flow rate, aquantity of the at least one set of at least two filtration surfaces,and combinations thereof.

Referring to FIG. 1, an exemplary embodiment of a filtration scheme isillustrated. For the exemplary embodiment illustrated in FIG. 1, astream 1 a of an aqueous liquid is provided, wherein the aqueous liquidhas been treated with a biocide. The stream 1 a is filtered with afiltration surface 10, creating a second stream 1 b. Once steady statefiltration (with respect to filtration surface 10) is achieved, thestream 1 a of the aqueous liquid is diverted (stream 1 a becomes stream2 a) to a filtration surface 20 that has a lower porosity than thefiltration surface 10, which is filtered thereby creating a third stream2 b. Optionally, upon reaching steady state filtration (with respect tofiltration surface 20), the stream 2 a of the aqueous liquid may bediverted (stream 2 a becoming stream 3 a) to a filtration surface 30,which is filtered thereby creating a fourth stream 3 b. At least aportion of any filtrate stream (streams 1 b, 2 b and 3 b) is returned tothe industrial process.

Referring to FIG. 2, another exemplary embodiment of a filtration schemeis illustrated. For the exemplary embodiment illustrated in FIG. 2, astream of an aqueous liquid (Fluid IN) is filtered with a filtrationsurface 110 having a given porosity. The filtrate (Fluid OUT) may befiltered full-flow with a filtration surface 120 that is less porousthan the filtration surface 110. Alternately, the filtrate may bereturned to the industrial process, and a side stream (an example of afiltration loop stream) may be filtered with filtration surface 130,wherein filtration surface 130 is less porous than filtration surface110.

Referring to FIG. 3, FIG. 3 illustrates an exemplary embodiment of afilter element 200 having at least two filtration surfaces. Theillustrated embodiment has three filtration surfaces 210, 220, and 230,each progressively less porous than the previous filtration surface in adownstream direction.

Referring to FIG. 4, FIG. 4 illustrates a second exemplary embodiment ofa filter element 200 having at least two sequential filtration surfaces210 and 220. The aqueous liquid enters (Fluid IN) the filter element 200and is filtered by the first filtration surface 210 having a givenporosity. The aqueous liquid then passes through the second filtrationsurface 220 and is returned to service in the aqueous cooling system(Fluid OUT).

For the embodiment illustrated in FIG. 4, an optional self-cleaningapparatus is built into the filter element 200, the self-cleaningapparatus able to vacuum the second filtration surface 220. Ascontamination collects on the second filtration surface 220, thepressure drop across the second filtration surface 220 and/or the filterelement 200 increases. Once the pressure drop reaches a setpoint, avacuum cycle is triggered. A rinse valve 270 opens to an atmosphericdrain (Drain) causing a drop in pressure within the filter element 200.The drop in pressure within the filter element 200 creates a backflushstream, thereby pulling the contamination from the second filtrationsurface 220. The aqueous liquid and contamination are sucked into theconduit 250 via the several nozzles 260. The aqueous liquid andcontamination exit the conduit 250 via either of two tubes 240 throughthe rinse valve 270 and out the drain. The cleaning apparatus thatincludes the two tubes 240, the conduit 250, and the several nozzles 260can be driven by a motor 300.

Optionally, one, two or more, including combinations of various devices,of the following devices may be included within the industrial process:a pressure monitoring device, a flow monitoring device, and a turbiditymonitoring device, each operably attached to the industrial process soas to provide input related to the biocide demand of the aqueous liquidwithin the industrial process. Optionally, a microbial monitoring devicemay be operably attached to the industrial process and provide furtherinput related to the biocide demand of the aqueous liquid within theindustrial process. Optionally, a biocide generating device may beoperably attached to the industrial system and controlled depending onthe measured biocide demand of the aqueous liquid within the industrialprocess. Non-limiting examples of biocide generating devices includeozone generators, ultraviolet radiation generators, and chlorinegenerators.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, the disclosure is directed toward a methodfor inhibiting microbial fouling in an aqueous liquid having a biocidedemand, which in certain embodiments takes the form of improvingefficiency in biocide dosing of the aqueous liquid. In certainembodiments according to the first, second, and third embodimentsdisclosed herein, the aqueous liquid is present in an industrialprocess, which in certain embodiments takes the form of an aqueouscooling system. In certain embodiments according to the first, second,and third embodiments disclosed herein, the aqueous cooling system is arecirculation-type aqueous cooling system. In other embodimentsaccording to the first, second, and third embodiments disclosed herein,the aqueous cooling system is a single-pass-type aqueous cooling system.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, the aqueous liquid having a biocide demandis treated with a biocide. In certain embodiments according to thefirst, second, and third embodiments disclosed herein, the treatmenttakes the form of dosing the biocide at a dosage rate. As it pertains tothis disclosure, “dosing” is a species of “treating.” Dosing refers tothe continuous, semi-continuous, or intermittent combining of a biocideand an aqueous liquid that has a biocide demand. Treatment refers tocombining of a biocide and an aqueous liquid that has a biocide demand,even if the combining does not happen in a continuous fashion or on aregular basis. In certain embodiments according to the first, second,and third embodiments disclosed herein, treatment occurs by introducinga biocide in solid, liquid, or gas form into an aqueous liquid. Incertain embodiments according to the first, second, and thirdembodiments disclosed herein, treatment occurs by physically introducinga biocide into an aqueous liquid (e.g., ultraviolet radiation). Incertain embodiments according to the first, second, and thirdembodiments disclosed herein, treatment occurs by generating a biocidein situ (e.g., ozone) from one or more precursors within an aqueousliquid.

The biocide may be one or a combination of more than one chemicalsubstances that are known to effectively kill microbiological organismsor at least inhibit microbiological function (e.g., growth and/orreproduction) when present in a second substance at a knownconcentration.

Non-limiting examples of biocides include oxidizing biocides,non-oxidizing biocides, or physical biocides. Physical biocides mayinclude, for example, steam sterilization or ultraviolet radiation.Oxidizing biocides include, but are not limited to, stabilized oxidantsand halogenated oxidants, which may include chlorine bleach; chlorine;bromine; iodine; materials capable of releasing chlorine, bromine,and/or iodine; inorganic peroxides; organic peroxides; chlorine dioxide;ethylene oxide; ozone; chloramines compounds; precursors thereof, andcombinations thereof. Non-oxidizing biocides include, but are notlimited to, quaternary ammonium compounds; glutaraldehyde; isothiazolin;2,2-dibromo-3-nitrilopropionamide; 2-bromo-2-nitropropane-1,3-diol;1-bromo-1-(bromomethyl)-1,3-propanedicarbonitrile;tetrachloroisophthalonitrile; alkyldimethylbenzylammonium chloride;dimethyl dialkyl ammonium chloride; didecyl dimethyl ammonium chloride;poly(oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylenedichloride; methylene bisthiocyanate; 2-decylthioethanamine;tetrakishydroxymethyl phosphonium sulfate; dithiocarbamate;cyanodithioimidocarbonate; 2-methyl-5-nitroimidazole-1-ethanol;2-(2-bromo-2-nitroethenyl)furan; beta-bromo-beta-nitrostyrene;beta-nitrostyrene; beta-nitrovinyl furan; 2-bromo-2-bromomethylglutaronitrile, bis(trichloromethyl)sulfone;S-(2-hydroxypropyl)thiomethanesulfonate;tetrahydro-3,5-dimethyl-2H-1,3,5-hydrazine-2-thione;2-(thiocyanomethylthio)benzothiazole; 2-bromo-4′-hydroxyacetophenone;1,4-bis(bromoacetoxy)-2-butene; bis(tributyltin)oxide;2-(tert-butylamino)-4-chloro-6-(ethylamino)-s-triazine; dodecylguanidineacetate; dodecylguanidine hydrochloride; coco alkyldimethylamine oxide;n-coco alkyltrimethylenediamine; tetra-alkyl phosphonium chloride;7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid;4,5-dichloro-2-n-octyl-4-isothiazoline-3-one;5-chloro-2-methyl-4-isothiazolin-3-one; 2-methyl-4-isothiazolin-3-one;precursors thereof; and combinations thereof.

Biocide demand of the aqueous liquid can be monitored using one or moreof various operating techniques, including but not limited to backwashcount, vacuum count, pressure drop across at least one filtrationsurface, and measurement of oxidation-reduction potential of at least aportion of the aqueous liquid. One typical technique involves measuringthe oxidation-reduction potential (“ORP”) of an aqueous liquid oraqueous liquid stream. A decrease in ORP can indicate an increase inmicrobial activity or a decrease in biocide concentration. In otherwords, a decreasing ORP typically indicates an increasing biocidedemand. A typical ORP-measuring device is an electrochemical measuringdevice that utilizes a probe. Exemplary embodiments of ORP-measuringdevices are available from any of several vendors including, but notlimited to, Hach Company, Loveland, Colo., and Rosemount Measurement,Chanhassen, Minn. In certain embodiments, ORP is monitored to determinethe biocide demand.

Alternatively or in addition to the above-described operating variables,biocide demand of the aqueous liquid can be measured by countingfiltration surface cleaning cycles. A cleaning cycle count (usually anaverage number of cycles per unit of time) can be correlated to thebiocide demand or a change of the biocide demand of the aqueous liquid.Non-limiting examples of cleaning cycles include backwash and vacuum(for appropriately equipped filtration surfaces).

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, a backwash count per period of time, orchange or lack thereof, is correlated to the biocide demand of theaqueous liquid. A typical backwash cycle isolates the filtrationsurface(s) to be backwashed from use, flows a non-contaminated liquid(usually purified water) in a counter-flow direction through thefiltration surface(s), and sends the counter-flowed liquid to a wastestream. Once backwashed, the filtration surface(s) can be returned toservice.

For certain embodiments according to the first, second, and thirdembodiments disclosed herein, the need for backwash is triggered on anas-needed basis (i.e., not scheduled in advance at set time periods)based on one or more of increased pressure drop across the filtrationsurface, decreased fluid flux across the filtration surface, orotherwise decreased performance of the filtration surface. For certainembodiments according to the first, second, and third embodimentsdisclosed herein, a high backwash count can indicate an increasedbiocide demand for aqueous liquids that are known to have microbialactivity. FIG. 5, described in more detail below, illustrates thephenomenon. A change in porosity of the utilized filtration surface(i.e., switching filtration surfaces) may affect the steady state (i.e.,take the process out of steady state) and affect the biocide demand andthe parameters that may indicate the biocide demand.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, one or more of the filtration surfacesthat are utilized include self-cleaning apparatuses comprising a vacuumsystem that removes at least a portion of the debris that has collectedon a particular filtration surface. For embodiments that utilize avacuum system, vacuum count per period of time, or a change or lackthereof, can be correlated to the biocide demand of the aqueous liquid.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, pressure drop, or a change in pressuredrop or lack thereof over time, across one or more filtration surfacescan be correlated to the biocide demand of the aqueous liquid. Incertain embodiments of the present disclosure, reaching a steady statewith respect to pressure drop across a filtration surface indicates thatthe stream being filtered should be diverted to a less porous filtrationsurface.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, at least a portion of an aqueous liquid isdiverted to a filtration surface or into a filtration loop, therebyproducing a stream. As it pertains to the present application,“diverting” means “causing to move to an identified location.” Suchdiversion can be performed using known techniques such as via pipingand/or pumping. In certain embodiments, the portion of the aqueousliquid may be diverted from a container into a conduit (e.g., pipe),from one conduit to another conduit, from a water source to a conduit,or any other suitable arrangement depending on the circumstances.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, filtration may be performed via one ormore techniques selected from the group consisting of dead endfiltration, flow-through filtration, cross-flow filtration, andcombinations thereof. Persons having skill in the art of filtration willreadily recognize these potential arrangements and the advantages anddisadvantages of each.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, a stream of an aqueous liquid is initiallyfiltered with a first filtration surface until a steady state isreached. An exemplary technique to determine steady state for thisfiltration is by monitoring pressure drop across the first filtrationsurface. Once the monitored pressure drop is reasonably constant for aconstant flow rate, the stream of the aqueous liquid is diverted to asecond filtration surface that has a lower porosity than the firstfiltration surface.

In certain embodiments according to the first, second, and thirdembodiments disclosed herein, a set of at least two sequentialfiltration surfaces are utilized to filter a stream of an aqueous liquidthat has a biocide demand. In certain embodiments according to thefirst, second, and third embodiments disclosed herein, the set includesat least two filtration surfaces that become less porous in a downstreamdirection. In certain embodiments according to the first, second, andthird embodiments disclosed herein, the set is present in a singlefilter element. In certain embodiments, the set includes three filterelements that are progressively less porous in a downstream direction.

EXAMPLES Example 1

Referring to FIG. 5, FIG. 5 illustrates the average number of backwashesper day for an 18-week span for a particular aqueous cooling system. Thefilter on this particular aqueous cooling system was installed with a100 micron screen. The number of backwashes indicates the number oftimes the filter performs the process of cleaning itself followingentrapment of solids by the filter. As shown in FIG. 5, after a periodof operation the backwash counts steadied to an average of 4.25backwashes per day. The filter was taken off-line for a short periodaround week 13 (hence 0 backwashes) and then recommissioned with asmaller porosity (50 micron) screen. The backwash counts thereafterincreased to an average of 6.6 per day suggesting that the filter wastrapping more debris and hence improving the water quality more thanwhen it had attained a steady state.

Example 2

Referring to FIG. 6, FIG. 6 illustrates an aqueous cooling system thatwas running without an installed filtration system (Test 1). Biocide wasdosed as a slug dose into the aqueous liquid, i.e., the biocide wasintroduced within a short period of time. As a consequence of thebiocide dosage, an increase in the oxidation reduction potential (“ORP”)of the aqueous liquid was observed. The observed ORP increase graduallydeclined over time, as the applied biocide was consumed. Consumption ofthe biocide occurred due to biocide demand, e.g., the presence ofinorganic or organic matter in the aqueous liquid, and physical loss dueto volatilization.

Subsequent to Test 1, a filter was installed on this system and Test 2was conducted. After a period of operation of the filter, which had twofiltration surfaces (a coarse screen followed by a 100 micron screen)within the filter element, a similar increase in ORP as seen in Test 1was observed for Test 2. However, the increase in ORP was significantlyhigher (approximately 30%) for Test 2 than for Test 1, even withoverlapping biocide pump run times for Test 1 and Test 2. A more gradualdecline in ORP was also observed for Test 2 as compared to Test 1. Inother words, an amount of biocide dosage with filtration issignificantly more effective in killing microbial growth than the sameamount of biocide dosage without filtration. The Test 2 results wereunexpected following the use of a filter, as compared to Test 1. Inother words, biocide treatment in combination with filtration,particularly dual-stage filtration, can aid with the inhibition ofmicrobial fouling beyond utilizing merely biocide treatment.

Any patents referred to herein, are hereby incorporated herein byreference, whether or not specifically done so within the text of thisdisclosure.

To the extent that the terms “include,” “includes,” or “including” areused in the specification or the claims, they are intended to beinclusive in a manner similar to the term “comprising” as that term isinterpreted when employed as a transitional word in a claim.Furthermore, to the extent that the term “or” is employed (e.g., A orB), it is intended to mean “A or B or both A and B.” When the applicantsintend to indicate “only A or B but not both,” then the term “only A orB but not both” will be employed. Thus, use of the term “or” herein isthe inclusive, and not the exclusive use. See Bryan A. Garner, ADictionary of Modern Legal Usage 624 (2d ed. 1995). Also, to the extentthat the terms “in” or “into” are used in the specification or theclaims, it is intended to additionally mean “on” or “onto.” Furthermore,to the extent that the term “connect” is used in the specification orthe claims, it is intended to mean not only “directly connected to,” butalso “indirectly connected to” such as connected through anothercomponent or components. In the present disclosure, the words “a” or“an” are to be taken to include both the singular and the plural.Conversely, any reference to plural items shall, where appropriate,include the singular.

All ranges and parameters disclosed herein are understood to encompassany and all sub-ranges assumed and subsumed therein, and every numberbetween the endpoints. For example, a stated range of “1 to 10” shouldbe considered to include any and all subranges between (and inclusiveof) the minimum value of 1 and the maximum value of 10; that is, allsubranges beginning with a minimum value of 1 or more (e.g., 1 to 6.1),and ending with a maximum value of 10 or less (e.g., 2.3 to 9.4, 3 to 8,4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10contained within the range.

The general inventive concepts have been illustrated, at least in part,by describing various exemplary embodiments thereof. While theseexemplary embodiments have been described in considerable detail, it isnot the Applicants' intent to restrict or in any way limit the scope ofthe appended claims to such detail. Furthermore, the various inventiveconcepts may be utilized in combination with one another (e.g., thefirst, second, and third exemplary embodiments may be utilized incombination with each other). Additionally, any particular elementrecited as relating to a particularly disclosed embodiment should beinterpreted as available for use with all disclosed embodiments, unlessincorporation of the particular element would be contradictory to theexpress terms of the embodiment. Additional advantages and modificationswill be readily apparent to those skilled in the art. Therefore, thedisclosure, in its broader aspects, is not limited to the specificdetails presented therein, the representative apparatus, or theillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the spirit or scope ofthe general inventive concepts.

We claim:
 1. A method of inhibiting microbial fouling, the methodcomprising: providing an industrial process containing an aqueous liquidhaving a biocide demand and a first filtration surface having a givenporosity and at least one operating variable selected from the groupconsisting of backwash count, vacuum count, oxidation-reductionpotential, and combinations thereof; treating the aqueous liquid with abiocide; determining the biocide demand of the biocide-treated aqueousliquid by monitoring at least one of the operating variables of thefirst filtration surface; providing a stream of the biocide-treatedaqueous liquid; filtering the stream of the biocide-treated aqueousliquid with the first filtration surface to produce a second stream as afiltrate stream that is initially returned to the industrial process,and continuing the filtering and returning of the filtrate stream untila steady state with respect to at least one of the operating variablesof the first filtration surface is reached; identifying that the steadystate with respect to at least one of the operating variables of thefirst filtration surface has been reached by measuring at least one ofthe operating variables, whereupon the stream of the biocide treatedaqueous liquid is diverted away from the first filtration surface to asecond filtration surface having a lower porosity than the firstfiltration surface; filtering the diverted stream with the secondfiltration surface to produce a third stream; and returning at least aportion of the third stream to the industrial process.
 2. The method ofclaim 1, wherein the stream of the aqueous liquid is either a full flowstream or a side stream.
 3. The method of claim 1, wherein theindustrial process is an aqueous cooling system.
 4. The method of claim1, wherein the identifying that the steady state with respect to atleast one of the operating variables of the first filtration surface hasbeen reached and the stream diversion from the first filtration surfaceto the second filtration surface is performed automatically.
 5. Themethod of claim 1, wherein the at least one operating variable isoxidation-reduction potential.
 6. The method of claim 1, wherein the atleast one operating variable is backwash count.
 7. The method of claim1, wherein the biocide is an oxidizing biocide.
 8. The method of claim7, wherein the oxidizing biocide is selected from the group consistingof chlorine bleach; chlorine; bromine; iodine; chlorine releasingcompounds; bromine releasing compounds; iodine releasing compounds;inorganic peroxides; organic peroxides; chlorine dioxide; ethyleneoxide; ozone; chloramines compounds; and combinations thereof.
 9. Themethod of claim 1, wherein the biocide is a non-oxidizing biocideselected from the group consisting of quaternary ammonium compounds;glutaraldehyde; isothiazolin; 2,2-dibromo-3-nitrilopropionamide;2-bromo-2-nitropropane-1,3-diol;1-bromo-1-(bromomethyl)-1,3-propanedicarbonitrile;tetrachloroisophthalonitrile; alkyldimethylbenzylammonium chloride;dimethyl dialkylammonium chloride; didecyl dimethyl ammonium chloride;poly(oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylenedichloride; methylene bisthiocyanate; 2-decylthioethanamine;tetrakishydroxymethyl phosphonium sulfate; dithiocarbamate;cyanodithioimidocarbonate; 2-methyl-5-nitroimidazole-1-ethanol;2-(2-bromo-2-nitroethenyl)furan; beta-bromo-beta-nitrostyrene;beta-nitrostyrene; beta-nitrovinyl furan; 2-bromo-2-bromomethylglutaronitrile, bis(trichloromethyl) sulfone;S-(2-hydroxypropyl)thiomethanesulfonate;tetrahydro-3,5-dimethyl-2H-1,3,5-hydrazine-2-thione;2-(thiocyanomethylthio)benzothiazole; 2-bromo-4′-hydroxyacetophenone;1,4-bis(bromoacetoxy)-2-butene; bis(tributyltin)oxide;2-(tert-butylamino)-4-chloro-6-(ethylamino)-s-triazine; dodecylguanidineacetate; dodecylguanidine hydrochloride; coco alkyldimethylamine oxide;n-alkyltrimethylenediamine; tetra-alkyl phosphonium chloride;7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid;4,5-dichloro-2-n-octyl-4-isothiazoline-3-one;5-chloro-2-methyl-4-isothiazolin-3-one; 2-methyl-4-isothiazolin-3-one;precursors thereof; and combinations thereof.
 10. The method of claim 1,wherein the biocide is ultraviolet radiation or steam sterilization. 11.The method of claim 1, wherein the biocide-treated aqueous liquid andthe diverted stream are filtered by dead end filtration, flow-throughfiltration, or a combination thereof.